The present invention relates to a toner for developing electrostatic latent images, and an image forming method and an image forming apparatus employing the same.
In recent years, along with development of digital image processing technology, in image forming methods utilizing an electrostatic latent image development system such as an electrophotographic system, digital system image formation has become mainstream.
In image forming methods utilizing the digital systems, an image comprised of dots as small as 1,200 dpi (dots per inch or the number of dots per 2.54 cm) is basically visualized, and high image quality technology is required which faithfully reproduces such minute dot image.
In order to effectively produce such high quality images, a decrease in the diameter of toner particles for developing electrostatic latent images has been carried out. In image formation utilizing an electrostatic latent image developing system such as an electrophotographic system, heretofore, a so-called pulverized toner, prepared as described below, has been mainly employed. Binder resins and pigments are mixed and kneaded. Powder prepared by pulverizing the resulting mixture is then classified by size. However, toner which is prepared employing such processes is limited in the decrease in the diameter of toner particles and uniform particle size distribution. Difficulties are accompanied to achieve a decrease in the diameter of toner particles, uniformity of the size distribution, as well as the particle shape. Consequently, it is difficult to sufficiently achieve higher image quality for images prepared by an electrophotographic system employing such pulverized toners.
In recent years, as means to achieve a decrease in the diameter of toner particles and uniformity of particle size distribution as well as the shape, polymerization method toners prepared employing a suspension polymerization method or an emulsion polymerization method have received increasing attention. These polymerization toners are prepared in such a manner that a dispersion prepared by uniformly dispersing monomers as a raw material in a water-based system undergoes polymerization to form toner. Several methods are feasible. Of these, the method which receives the highest attention is one in which resinous particles, prepared employing a suspension polymerization method or an emulsion polymerization method as well as colorant particles, are subjected to coalescence (salting-out and fusion). The aforesaid method has been studied for practical use but the aspect of its production engineering is still in the stage of development.
On the other hand, widely employed as a system for fixing toner images formed on an image forming support (being a transfer material) such as a paper sheet is a heating roller fixing system in which fixing is carried out by allowing the aforesaid image forming support carrying images to pass between a heating roller and a pressure roller.
However, when the heating roller fixing system is employed in combination with the polymerization method toner in which toner particles have a small diameter and the particle size distribution as well as the shape is uniform, problems occur in which since toner particles are not capable of being sufficiently deformed to conform to the unevenness of the paper and the heating roller surface, insufficient fixing results.